#parser #peg #parser-generator #grammar

macro pegy-derive

A derive based parser generator

3 releases

0.1.2 Nov 9, 2023
0.1.1 Oct 24, 2023
0.1.0 Oct 24, 2023

#46 in #peg


Used in pegy

MIT license

32KB
696 lines

Pegy - derive based Parser in Rust

Docs Crates.io Crates.io

Features

  • derive based parser generation
  • async api for parsing
  • parse input from str, async readers or custom input types.
  • AST generation on the run
  • meaningful error messages for errors in grammar definition
  • supports no_std

MSRV

The current MSRV supported is 1.75

Example

use pegy::Parse;

#[derive(Debug, Default, Parse)]
#[grammar($item0:['a'-'z''A'-'Z''0'-'9'])]
pub struct AlphaDigit(char);

#[derive(Debug, Default, Parse)]
#[grammar($item0:['0'-'9'])]
pub struct Digit(char);

#[derive(Debug, Default, Parse)]
#[grammar(!Digit $item0:AlphaDigit+)]
pub struct Ident(Vec<AlphaDigit>);

pub fn main(){
    let re: pegy::Result<Ident> = pegy::parse_blocking::<Ident, _>("myIdent");
    assert!(re.is_ok());
}

Comparison with similar traits

crate action code integration input type streaming input
pegy in grammar proc macro(derive) &str, AsyncRead, custom Yes
peg in grammar proc macro(block) &str, &[T], custom No
pest external proc macro(file) &str No

Expression Reference

Term

  • "some string" - string literal: matches a str slice. returns &'static str.
  • 'c' - character literal: matches a character. returns char.
  • Ident - rule: matches a Parse rule. It must be a valid type and imlplements pegy::Parse. returns Ident type.
  • ['a'-'z''A'-'Z''$'] - character class: matches a range of characters. returns char.

Quantifier

  • ? - optional: matches zero or one term. returns Option<T>
  • * - repeat: matches zero or more terms. returns Vec<T>
  • + - repeat atleast: matches one or more terms. returns Vec<T>.
  • {min, max} - repeat range: matches at least min and at most max number of terms. returns Vec<T>

Special

  • $ident:term - field binding: bind the result of the term to the field ident of result. returns ().
  • ( alternatives ) - group: matches the terms and returns a Span.
  • terms | terms | terms - alternatives: trys to match the first terms, if failed, matches the second one and so on until a match is found. returns a Span.
  • !term - negative lookahead: matches the term without consuming any characters.
  • _ term - quiet: matches the term and returns ().

Dependencies

~235–680KB
~16K SLoC